The present invention relates to apparatus and methods for automatically inspecting dovetails on turbine rotors without rotating the turbine rotor and particularly relates to an inspection system having a link system rotatably mounted about a rotor shaft and carrying a transducer for determining defects in the dovetails of the rotor wheels.
Currently, defects in the dovetails of rotors, e.g., tangential entry dovetails on steam turbine rotor wheels, are detected by manually moving an ultrasonic transducer about a stationary wheel on the turbine rotor shaft to interrogate the dovetail. The transducer is held in place by a rigid fixture which helps to keep it at a constant radial position. For each area of the dovetail geometry being inspected, one scan about the rotor is completed with the transducer held at a predetermined radial position. Proper radial positioning of the transducer on the face of the wheel is critical to assure the intended inspection area is being examined. This manual method disadvantageously requires the operator to be manually manipulating the transducer while observing a CRT display for signals indicative of defects.
An alternative method for identifying defects is to use a phased array and automated ultrasonic transducer (UT) dovetail inspection system. Such systems include an encoder feedback into a computer to collect the information needed to perform the test. The test, however, requires the turbine rotor to be placed on rollers or rolling devices so that the rotor may be turned for the inspection. Phased-array automated UT dovetail inspection systems of that type are not cost-effective for smaller units and require substantial labor and time to set up and perform the automated inspection.
Another prior inspection system is described and illustrated in U.S. Pat. No. 5,623,107. In that system, an inspection device having electric motor-driven magnetic wheels for magnetic attachment of the device to the cylindrical surface between the wheels of the turbine rotor is disclosed. While this system offered certain advantages, the complexity of set-up, the test time and maintenance of the system inhibited widespread adoption and use of such system.